Sudden cardiac death

Sudden cardiac death, without any warning that there might be problems with the heart, frequently occurs in young athletes. This raises the question whether and how often young athletes should be screened for cardiac anomalies.

Transcript

Norman Swan: Hello from me, Norman Swan. Today on the Health Report we get to the bottom of that itch which has been driving you nuts. And if you haven't got an itch I guarantee you will have one by the end of the show. Find out why one of the most common medications used to help itching is pretty useless a lot of the time, and why you should be taking a bath rather than a shower. We'll have that skin of yours glistening.

For all our insomniac listeners, the opportunity to join a trial of online treatment for sleeplessness, and no it's not a continuous feed of Radio National, shame on you for even thinking it. Air pollution and your heart, and rare but high impact tragedies.

Journalist [archival]: Susan Taylor had been in training for over a year for the charity 21-mile swim across the English Channel.

Susan Taylor [archival]: I remembered back to a childhood moment when a lady said to me when I was going to a swimming gala, 'Will you swim the channel when you're older?' And I can remember looking up to the old lady and nodding my head up and down and saying, yes, I would. And for some reason I decided I hadn't achieved that goal, so I needed to go and do it, so I decided to charter a boat and swim the channel.

Journalist [archival]: Susan set off on the charity swim but got into difficulty near the French coast. She was then airlifted to hospital where she died.

Norman Swan: It's not clear what killed cross-channel swimmer Susan Taylor last week but when a young person dies suddenly and unexpectedly during sport or exercise, there's an enormous impact. Usually the cause is the heart and there's been a controversial push to screen young people before they take up high-exertion sports.

Someone who's a world authority in this area is Dr Mark Link, a specialist in abnormal heart rhythms and Professor of Medicine at Tufts Medical Center in Boston. One major interest of Dr Link's is a disastrous condition called commotio cordis.

Mark Link: Commotio cordis occurs when an individual gets struck in the chest by a baseball, hockey puck or other round spherical object and dies suddenly, right on the playing field. And it happens probably about 15 to 20 times a year in the States.

Norman Swan: So it's a rare phenomenon.

Mark Link: It's a rare phenomenon, as is sudden death in athletes, it's really quite a rare phenomenon relative to sudden death in individuals with coronary disease.

Norman Swan: What causes this problem? It has to be a round object?

Mark Link: Yes, it has to be a spherical object of some ilk. What we found is there's a number of factors that have to be just perfect in order to induce ventricular fibrillation or sudden death. Perhaps the most important is timing relative to the cardiac cycle. The strike has to occur on the upslope of the T-wave over a narrow 20-millisecond window. That's about 1% to 2% of the cardiac cycle.

Norman Swan: So if you think of an ECG trace there are several wave forms. There's the first waveform is a P-wave, then it goes Q, R, S, T, and T is the last little blip before you go into the next heartbeat, and what you're saying is…so after the heart has contracted and it's in the recovery phase, if you get hit by the ball at that point, that's the killer.

Mark Link: That's correct, and it's during that time period of repolarisation that there is a vulnerable time spot, that if you get hit by an object at that time period you can have the induction of ventricular fibrillation.

Norman Swan: You'd have to be very unlucky.

Mark Link: Extremely unlucky, because it's not only the timing of the impact it's the location of the impact. We found in our experimental model that the location must be directly over the centre of the left ventricle. If you move so much as one to two centimetres away from the centre, the incidence of VF drops off dramatically.

Norman Swan: So what it causes is this quivering of the heart similar to the thing that kills you with a heart attack, there's electrical chaos.

Mark Link: Yes, it's the same ventricular fibrillation you'd see with sudden cardiac death in individuals with heart disease, with individuals with myocardial infarctions.

Norman Swan: So if you actually were to look at your chest in the mirror, where is your left ventricle?

Mark Link: The left ventricle is to the left of the sternum. The heart twists during development and moves over to the left. So if you look at an x-ray, the right side of the chest has no heart in it whatsoever, the entire heart is in the left side of the chest, and so that's where the impact has to occur.

Norman Swan: And does the impact have to be hard?

Mark Link: What we found in our experimental model is that 40 mile an hour baseballs were the most damaging, the most likely to produce ventricular fibrillation. 20 mile an hour impacts barely ever caused commotio cordis or ventricular fibrillation, 30 miles an hour probably about 30%, 40 miles an hour about 50%. And it starts to drop off at 50, 60 and 70 miles an hour, but largely that's because at these impact velocities you get myocardial contusions, valve ruptures, myocardial ruptures, and so it no longer is commotio cordis, it's contusio cordis, which is what you see with bomb blasts and motor vehicle accidents.

Norman Swan: Does it happen in squash, or does it have to be a certain size of ball?

Mark Link: Interestingly it does not happen with pneumatic balls, they have to be hard enough in order to penetrate through the ribs or penetrate and cause the rib deformation. And the safety baseballs, the kind you use in T-ball and up to six- and seven-year-olds almost never caused VF in our model.

Norman Swan: And have you had many cases in cricket?

Mark Link: There have been cases in cricket. I know of four or five that are in the registry from cricket.

Norman Swan: Is there any way of preventing this? It just seems like an extraordinary conjunction of circumstances would result in somebody's death.

Mark Link: Prevention can be attained. It will never be completely 100%. There are a number of ways. One is coaching techniques and rules techniques that prevent individuals from blocking the ball with their chest, and this is really relevant for many sports, including baseball and lacrosse, where individuals are taught to block the ball with their chest. So I think that would be one thing.

Two, the hardness of the ball makes a difference. So for younger kids playing baseball they should use age-appropriate safety baseballs. And finally, chest protectors…about a third of the individuals that are in competitive sports that have a commotio cordis event were wearing chest protectors, yet they did not prevent commotio cordis. I do think that manufacturers have taken heart to this and they are probably or at least attempting to build better chest protectors, but whether they actually are better has not been proven yet.

Norman Swan: You also have an interest in sudden death per se. Is a sudden death always ventricular fibrillation?

Mark Link: What we call sudden arrhythmic death is the one I'm more interested in. This is not a condition confined to athletes. Almost all causes of sudden death, not only in the young but in the old, are due to some underlying cardiac condition. In the individuals aged over 35 to 40 it's almost always coronary artery disease, but in individuals under 35 it typically is a congenital problem, something they're born with, something like hypertrophic cardiomyopathy, the long QT syndrome, Brugada syndrome.

Norman Swan: So, just to explain, the cardiomyopathy is where you've got thickened abnormal heart muscle and that can make you susceptible to an arrhythmia, and the long QT is where you've got abnormal electrics in the heart.

Mark Link: That's correct.

Norman Swan: There's been this huge debate about whether or not kids going into athletics, particularly elite athletics, should be screened for the risk of sudden death. People who argue for it obviously say it's going to save lives, people who argue against it say you find so many instances where it's not a problem and you've condemned somebody to endless investigations and anxiety.

Mark Link: I don't know if the debate is as vigorous in Australia as it is here, but here it's very vigorous. Everyone wants to save kids from dying, and the issue is how can you do that? There has been a movement based on data from Italy that with screening, and especially including EKG screening, you can pick up some of these diagnoses. And when you pick up some of these diagnoses, if you prevent them from playing you will prevent them from dying. This is an unproven assumption in my mind.

Norman Swan: And in that Italian study they made a lot of mistakes with the electrocardiogram analysis, did they not?

Mark Link: Well, 10% of the Italian athletes screened had abnormal EKGs and went on to get echoes, 10%. That's a huge number, and especially when you consider that Italian athletes are genetically homogenous, especially compared to conditions we have here in the States where there are many more African American and other nationalities that have a much higher incidence of abnormal EKGs.

Norman Swan: So what's your position on this?

Mark Link: My position is that there is inherent risk in sports and there's inherent benefit in sports, and we don't want to unnecessarily penalise those who have a grey diagnosis, and in my mind EKG screening will lead to a vast number of grey diagnoses; do they really have a disease, do they really not? And so at this point I am not a fan of universal EKG screening. I think it deserves more study, I think it deserves thought, but I think there are many problems with this approach.

Norman Swan: And you've been looking also at air pollution and its effects on the heart's rhythm.

Mark Link: We have a particular interest in the acute triggering of both ventricular and atrial arrhythmias with air pollution.

Norman Swan: So just to explain, the ventricles of the lower chambers of the heart, the atria, are the top chambers. The ventricular arrhythmias are the ones that kill you, but the atrial ones are not too good to have either.

Mark Link: That's correct. The most common atrial arrhythmia is atrial fibrillation, which is not good because it leads to stroke and heart failure. And ventricular arrhythmias are ventricular tachycardia and ventricular fibrillation, which we just talked about. We work with the Harvard School of Public health that does hourly monitoring of air quality levels in the Boston area, and we have both a retrospective and a prospective study where we've asked individuals with defibrillators to join the study. The defibrillators not only will recognise an acute arrhythmia, both atrial and ventricular…

Norman Swan: These are people with implanted defibrillators?

Mark Link: That's correct, an implantable defibrillator. So they not only recognise what the rhythm is, they'll treat the ventricular arrhythmia, saving your life, but then they will document the date, the time, the second and what the arrhythmia was.

Norman Swan: So these are people susceptible to it, they've got heart failure or they've had a heart attack with ventricular fibrillation and they put in an implantable defibrillator to prevent them having another episode of potentially sudden death.

Mark Link: That's correct.

Norman Swan: So here's a golden opportunity to monitor it incredibly accurately.

Mark Link: Yes. So we get down to the second initiation of atrial and ventricular arrhythmias, and with hourly air pollution we can actually…with using the individuals as their own case-control, determine whether acute spikes in air pollution will cause acute arrhythmias.

Norman Swan: And?

Mark Link: They do, they cause a slight increase in ventricular arrhythmias, but remarkably a dramatic increase in atrial fibrillation, and it correlates quite closely within two hours of air pollution going up, the incidence of A fib will increase.

Norman Swan: So is there a concomitant increase in stroke then with air pollution?

Mark Link: There is. That wasn't the purpose of our study or wasn't the endpoint of our study, but another one of our colleagues we work with, using the same database of air quality, has shown an increase in strokes with air pollution.

Norman Swan: So the weight could work is air pollution causing the top chambers of your heart to quiver, clot gathering there, and stroke.

Mark Link: That's exactly correct.

Norman Swan: Why does air pollution do this?

Mark Link: When you go into air pollution areas, when you're breathing small particles into your lungs, that promotes a systemic inflammatory response.

Norman Swan: So your immune system reacts and everything gets very irritable.

Mark Link: I think that's one of the drivers of A fib, I think it also produces some coronary ischaemia, air pollution quality. And it also affects your lungs, you can get more bronchospasm.

Norman Swan: Dr Mark Link is an electrophysiologist and Professor of Medicine at Tufts Medical Center in Boston.